苯亚硝基甲烷质子转移反应的动力学研究。对硝基烷异常起源的启示。

Kinetic study of proton-transfer reactions of phenylnitromethanes. Implication for the origin of nitroalkane anomaly.

机构信息

Department of Chemistry and the Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro, Toshima-ku 171-8501 Tokyo, Japan.

出版信息

J Org Chem. 2011 May 20;76(10):3937-45. doi: 10.1021/jo200383f. Epub 2011 Apr 12.

DOI:10.1021/jo200383f

PMID:21486082

Abstract

Measurements of rate constants and substituent effects for three important elementary steps of proton-transfer reactions of phenylnitromethane were reported. The Hammett ρ values for the deprotonation of ArCH(2)NO(2) with OH(-), protonation of ArCH═NO(2)(-) with H(2)O, and protonation of ArCH═NO(2)(-) with HCl were determined in aqueous MeOH at 25 °C. Comparison of these experimentally observed ρ values with those calculated at B3LYP/6-31G* revealed that aci-nitro species (ArCH═NO(2)H), which is formed on the O-protonation of ArCH═NO(2)(-), does not lie on the main route of the proton-transfer reaction. Analysis of the Brønsted plot implies that the proton-transfer reaction of most XC(6)H(4)CH(2)NO(2) exhibits nitroalkane anomaly, but not for p-NO(2)C(6)H(4)CH(2)NO(2), and that the transition state charge imbalance is an origin of anomaly.

摘要

测定了苯基亚硝甲烷质子转移反应三个重要基元步骤的速率常数和取代基效应。在 25°C 的甲醇水溶液中测定了 ArCH(2)NO(2)与 OH(-)的去质子化、ArCH═NO(2)(-)与 H(2)O 的质子化以及 ArCH═NO(2)(-)与 HCl 的质子化的哈米特 ρ 值。将这些实验观察到的 ρ 值与 B3LYP/6-31G*计算得到的 ρ 值进行比较表明，酸式硝基物种（ArCH═NO(2)H）不是 ArCH═NO(2)(-)的 O-质子化的主要途径上形成的。布仑斯特图的分析表明，大多数 XC(6)H(4)CH(2)NO(2)的质子转移反应表现出硝基烷异常，但对 p-NO(2)C(6)H(4)CH(2)NO(2 则不然，而且过渡态电荷不平衡是异常的起源。